Several processes have been proposed or used commercially for the liquefaction of low molecular weight gases.
An article by K. Clusius, "A plant for the production of Liquid Hydrogen with Neon as an Intermediate Working Substance," Zeitschrift for Die Gesamte Kalte-Industrie 39, No. 6, 14-7 (1933), discloses a process for the liquefaction of hydrogen utilizing a high pressure Linde cycle using evacuated liquid air or liquid nitrogen as the precoolant and high pressure neon as an intermediate working fluid and six atmosphere hydrogen expansion for final refrigeration requirements. The article does not teach the use of expansion engine cycles such as are used in the Claude or Brayton cycles.
U.S. Pat. No. 3,180,709 discloses a process for the liquefaction of gases, e.g. hydrogen, helium and neon, using multiple isenthalpic expansions (J-T valves) in parallel combination with an expander.
U.S. Pat. No. 3,473,342 describes a process specifically to liquefy large quantities of neon by cooling compressed gaseous neon with liquid nitrogen, expanding a portion of the cooled compressed neon in a turbo-expander to provide intermediate refrigeration and expanding the remaining neon through J-T expansion to produce liquid neon. Basically, the cycle is a single engine Claude refrigerator.
U.S. Pat. 3,609,984 discloses a process for the liquefaction of gases such as hydrogen, helium and neon. Basically, the process achieves the liquefaction by compression of the gas to a pressure such that upon isobarically cooling the compressed gas, a temperature above the critical temperature of the gas is reached at which the gas can be isentropically expanded to yield substantially a single liquid phase at atmospheric pressure; then isobarically cooling the gas, followed by isentropically expanding the cooled gas through a work engine thereby producing a substantial liquid phase.
U S. Pat. No. 3,992,167 and an article by C. F. Baker, "Hydrogen Liquefaction Using Centrifugal Compressors", Hydrogen Energy progress lV, Volume 3, pargamon Press (1982) disclose a process for the liquefaction of hydrogen using a second component admixed with hydrogen in order to utilize centrifugal compression. Both references teach the need for higher molecular weight gases in order to utilize centrifugal compression.
U.S. Pat. No. 4,498,313 discloses a helium refrigeration process and apparatus which includes a neon gas-refrigerating and liquefying circuit which precools the helium gas and uses a turbine type compressor. The process also utilizes liquid nitrogen for additional refrigeration duty.